CVE-2024-50263 fork: only invoke khugepaged, ksm hooks if no error
A flaw in the Linux kernel's fork operation could lead to a null pointer dereference when memory allocation fails, causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-50263?
CVE-2024-50263 is a high-severity vulnerability in Linux kernel, published on 11 Nov 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
fork: only invoke khugepaged, ksm hooks if no error
There is no reason to invoke these hooks early against an mm that is in an incomplete state.
The change in commit d24062914837 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()") makes this more pertinent as we may be in a state where entries in the maple tree are not yet consistent.
Their placement early in dup_mmap() only appears to have been meaningful for early error checking, and since functionally it'd require a very small allocation to fail (in practice 'too small to fail') that'd only occur in the most dire circumstances, meaning the fork would fail or be OOM'd in any case.
Since both khugepaged and KSM tracking are there to provide optimisations to memory performance rather than critical functionality, it doesn't really matter all that much if, under such dire memory pressure, we fail to register an mm with these.
As a result, we follow the example of commit d2081b2bf819 ("mm: khugepaged: make khugepaged_enter() void function") and make ksm_fork() a void function also.
We only expose the mm to these functions once we are done with them and only if no error occurred in the fork operation.
Which versions are affected by CVE-2024-50263?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-50263?
Apply the vendor's patch.
Is CVE-2024-50263 being exploited?
There is no known exploitation of CVE-2024-50263 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-50263, DEBIAN-CVE-2024-50263, GHSA-5mmf-rjpr-m4cj, UBUNTU-CVE-2024-50263.